1. Field of the Invention
The invention relates to heavy alloys of tungsten and methods of producing such alloys.
2. Description of the Prior Art
Tungsten heavy alloys, which are of great value in counter weights for aircraft, in ballistics, and in other applications, are conventionally produced by liquid phase sintering of mixed elemental powders. Alloys produced by this method are generally two-phase composites consisting of rounded tungsten grains dispersed in an alloy matrix.
The mechanical properties of tungsten heavy alloys are strongly dependent upon their specific microstructural features: for example, the grain size, contiguity, dihedral angle and the volume fraction of the tungsten phase. For a given tungsten content, the optimal microstructure exhibits low contiguity, small grain size, and strong W-W grain boundary and W-matrix interface.
There are serious drawbacks associated with the fabrication of tungsten heavy alloys by liquid phase sintering, one of the principal problems being that such alloys almost always exhibit excessive grain growth.
Solid state sintering is a known means for obtaining finer alloy microstructures. In fact, the microstructure of solid state sintered heavy alloys using tungsten powder of spherical morphology exhibit low contiguity and finer grain size in comparison with materials produced by liquid phase sintering. However, the mechanical properties of these solid state-produced materials, especially their ductility, is very low. The probable cause of low ductilities in these materials is the weak interphase and interface boundaries of their composite microstructure.
Improved tungsten heavy alloys and improved methods for producing the same are required.